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A very basic and easy to make arduino PC oscilloscope.

Features:

  • 50K samples/second
    (actually it can go up to 110K but the signal will become noisy)
  • Auto trigger
  • Frequency counter
  • Reasonably accurate voltage readings (depending on the accuracy of the resistors used for the voltage dividers)
  • Optional: selectable voltage range: 5V, 6.6V, 10V, 20V

You'll need:

      • An Arduino Leonardo or Arduino Micro
      • 2 crocodile clamps
      • a 0.1µF capacitor (optional)
      • a 5.1V zener diode (optional)
      • a pc with Processing

      For the voltage dividers (optional, if you want to measure than 5V or want selectable range):

      • 2 two-pole dual throw switches
      • two 3K resistors
      • two 1.5K resistors
      • one 1K resistor
      • a small perfboard or breadboard


      If you only need to measure op to 5V, you can skip the voltage dividers and connect the probes directly to GND and A1. You'll have to modify the code a bit:

      In the arduino code, replace:

      ADMUX =  B00000000;         // select external reference and port 5 (A0)

      with:

      ADMUX =  B01000000;         // select internal reference (Vcc - 5V) and port 5 (A0)

      In the processing code, replace:

      // read switch position & set voltage range
       boolean switch1=((buffer[writeIndex*2]&(byte)8)==8);                                                 
       boolean switch2=((buffer[writeIndex*2]&(byte)4)==4);
       if (!switch1&&!switch2) voltageRange=20;
       if (!switch1&&switch2) voltageRange=10;
       if (switch1&&!switch2) voltageRange=6.64;
       if (switch1&&switch2) voltageRange=5;

      with:

      voltageRange=5;

      Step 1: Adding Voltage Dividers

      The circuit show above consists of:


      On the left: a 1:4 voltage divider between the probe and A1

      This will bring the voltage down to 1/4 of the input voltage. The analog pins can handle 5V, so this will allow for voltages up to 20V.

      Note that there are 2 input channels in the picture of the breadboard. Adding an extra channel slowed down the sampling rate dramatically (because continuous mode can't be enabled on the ADC), so I decided to leave it out in the final code.

      On the right: a switched voltage divider between 5V and the Analog Reference (AREF) pin
      You can use the switches to set the measuring range: 5V, 6.64V, 10V of 20V

      How this works:

      If configured to 'external reference', the ADC compares the voltage of the analog inputs with AREF, instead of 5V.
      Here's an example: suppose the probe is measuring 5V. The voltage on the A1 will be 5V/4 = 1.25V

      • If both switches are off, the voltage on the AREF pin is 5V.
        The ADC will read 1.25/5 = 25%
      • If switch 1 is off and switch 2 is on, the voltage on AREF is 2.5V
        The ADC will read 1.25/2.5 = 50%
      • If switch 1 is on and switch 2 is off, the voltage on AREF is 1.66V
        The ADC will read 1.25/1.66 = 75%
      • If both switches are on, the voltage on AREF is 1.25V
        The ADC will read 1.25/1.25 = 100%

      The second pole of each switch is connected to a digital input. We can read this pin to automatically adjust the voltage scale.

      A capacitor between the probe and ground
      Might not be necessary, but for some reason some pc's measure a lot of noise without it. The capacitor will solve that, but may slightly affect the signal when measuring high frequencies.

      A zener between A0 and ground
      To protect the arduino a little from overvoltage or reverse voltage (thanks, tttapa, for the tip!)

      Be careful:

      • If the analog reference is set to internal (default) while you are supplying voltage to the AREF pin, the arduino could get damaged. I did that, and it didn't damage mine, but better be safe and upload the proper code before connecting AREF.
      • the analog inputs can't handle negative voltages.
      • Don't exceed 5V on the arduino pins. It's probably a good idea to test the circuit with a voltage below 5V, so

        you don't damage the arduino in case the voltage divider on A1 was wired incorrectly.

      The arduino code was based on this excellent article:

      http://meettechniek.info/embedded/arduino-analog.html

      Good luck!
      Bram

      Step 2:

      <p>cool stuff</p>
      exactly 44 thousandth view 44000
      <p>Hello,</p><p>I do not own a Micro or Leonardo, but I own an Uno. Will this instructable still work with the Uno?</p><p>Thanks.</p>
      Hello Ganesh,<br>It will work, but the sample rate would be limited by the serial speed.<br>(You'll need about 800.000 bps for 50K samples/sec. I don't know how fast the uno's serial can go.)<br><br>Regards,<br>Bram<br><br>
      <p>it can go upto 115200baud or bps</p>
      <p>Someone on <a href="http://arduino.stackexchange.com/questions/296/how-high-of-a-baud-rate-can-i-go-without-errors">this thread</a> claims his UNO goes up to 2Mbps. <br>Perhaps the 115200baud is a limitation of arduino IDE's serial monitor?</p>
      <p>see, the arduino CAN do 921600 baud, just the ide only goes to 115200</p>
      <p>&gt;Perhaps the 115200baud is a limitation of arduino IDE's serial monitor?</p><p>it indeed is. HyperTerminal can go upto 921600 baud. But anything above 115200 baud is lossy and subject to line interference so it is hardly ever used. </p>
      <p>Mr. Bram, how you can assumption 50k sps need 800.000 bps? can you explain to me? thx</p>
      <p>Hello Nsoclo,</p><p>50,000 samples/sec * 16 bits/sample = 800,000 bits per second.</p><p>Regards,<br>Bram</p>
      <p>16 bits/sample ? in specification, Arduino ADC is 10 bit. why it can 16 bits/sample?</p><p>tanks you very much Sir !</p>
      <p>You're right, one sample is 10 bits, plus two bits for the switches, but it is sent as 2 bytes for simplicity (and because it doesn't matter on an arduino micro, where the ADC rate is the limiting factor).</p>
      <p>thanks your information Sir, its helpfull.</p><p>Regards,</p><p>Narto</p>
      <p>Nice work with the scaling/ranging. I've recently started noodling around with the serial plotter tool in place of processing, and it was relatively easy to emulate a triggered sweep function with a simple threshold triggered loop:</p><p><a href="https://edwardmallon.wordpress.com/2016/08/15/using-the-arduino-uno-as-a-basic-data-acquisition-system/" rel="nofollow">https://edwardmallon.wordpress.com/2016/08/15/usin...</a><br><br></p>
      <p>An interesting topic. Nice job!</p>
      <p>I like your oscilloscope! But I think it's better to show the result with a LCD ;)</p>
      <p>Hi,</p><p>I get an error on this line</p><p>serial = new Serial(this, Serial.list()[keyCode-112], serialBaudRate);</p><p>errpr: ArrayIndexOutOfboundsException:-122</p><p>Im on OSX 10.11.1 thanks!</p>
      <p>Hell Pumidoil,<br>I can't test on Mac, but try pressing Fn together with the function key to select the serial port. Maybe Mac defaults to Fn lock.<br>If that doesn't work, replace (in processing):</p><blockquote>serial = new Serial(this, Serial.list()[keyCode-112], serialBaudRate);</blockquote><p> with:</p><blockquote>serial = new Serial(this, COM3, serialBaudRate); <br>//(replace COM3 with the right port)</blockquote><p>Let me know if it still doesn't work.</p>
      <p>Hi,</p><p>Thanks for fast reply! You just gave me the idea. It's the Fn button that freezes the program. </p><p>I used onscreen keyboard to select COM port. Now it works flawlessly.</p>
      <p>Nice Instructables, i reproduce it and it is working as expected, good work and thank you, i learned a lot</p>
      <p>Can you please explan how did you get 50k samples per sec?<br>When I log raw data from serial port I can get max 12k samples per sec.<br>Thank you In advance.</p>
      <p>Hi Brajamobil,</p><p>Are you using analogRead? If so, have a look at: <a href="http://meettechniek.info/embedded/arduino-analog.html">http://meettechniek.info/embedded/arduino-analog.h...</a>, and the atmega datasheet.<br><br>The frequency can be increased by:<br>- lowering the prescaler of the ADC, so it will run at a higher frequency. <br>- setting the ADC to continuous mode, with an interrupt to read the data into an array.<br>- sending multiple samples at a time (because each serial.write command has some overhead)</p>
      <p>Hi Bram,</p><p>I'm using your &quot;scope.ino&quot;. In your code I don't see 50K samples going over<br>serial port. I have installed serial logger to see If I am missing something.<br>I am not questioning ADC sampling at 50K, just transferring that data over serial line. Serial baud is not enough.</p>
      <p>Sorry, I misunderstood. <br>What exactly does the serial logger count? 12K bytes/sec?<br>Have you tried the processing sketch?</p>
      <p>I tried your processing sketch. Refresh rate is not high because serial line is slow by design. You can't trasfer 50K samples over it. Search google for explanation of baud. After that please explain how did you manage to transfer that amount of data over it. If you can't then please correct your instructable.</p>
      <p>Hey Brajamobil,</p><p>Apparently the Micro and Leonardo don't use the UART for USB communications. They ignore the baudrate set in serial.begin(xxx), and allow for much faster speeds (up to 12Mbit/s). <br>Thanks for pointing this out. I've updated the instructable.</p>
      Hii first of all thanks for this instructables . I am facing problems in measuring voltage more than 5volts it losts its accuracy below 5 volt it works fine but when I set switches on like 20v confriguation and it is also showing 20 volt on processing output but after this I applied 11v on probes it shows around 19 volts
      <p>Hi Akshay,</p><p>If you have a voltmeter you could try measuring:<br>- between A0 and GND: should be 1/4th of the voltage at the probe<br>- between AREF and GND: depending on the switches, this should be 5V (20V scale), 2.5V (10V scale), 1.66V (6.66V scale) or 1.25V (5V scale)</p><p>If all these are correct, perhaps pins D3 or D4 are connected to the wrong poles of the switches, selecting the wrong voltage scale. You can invert pins D3 and/or D4 in processing:<br>boolean switch1<b>=!</b>((buffer[writeIndex*2]&amp;(byte)8)==8);<br>boolean switch2<b>=!</b>((buffer[writeIndex*2]&amp;(byte)4)==4);</p><p>Good luck! Let me know if it still doesn't work.</p>
      Thanks for the reply but unfortunately it doesn't work <br>1. I've check voltage between A0 &amp; Gnd it is giving exactly 1/4th of voltage <br>2. I've also checked votage at Aref pin it also as you've mentioned <br>3. At last I ve modify code according to you but it give me wrong values <br>But it is working great below 10 volts but when I set switches to 20 volt mode it gives unwanted noise which was not present in any other confriguation <br>
      <p>Hi Akshay,<br>Strange. The only thing I can think of is that AREF is left floating when both switches are on. Have you tried connecting AREF directly to the arduino's 5V pin? (this should give you the 20V range)</p>
      You can see this unwanted noise but must tell you that lower than 10v it works very well
      <p>What is the maximun frequency it can measure? </p>
      <p>In theory, half the sampling rate, about 25KHz. But you won't be able to distinguish the shape of the wafevorm anymore.</p>
      <p>With only two samples you can't represent any signal accurately unless it's a perfect square wave. In practice you need at least 10 samples of each period of the signal in order draw it accurately enough on the screen (by joining the dots), which means the maximum frequency is around 5Khz. Still pretty good for many low frequency applications though.</p>
      <p>Bram super man erg erg tof</p><p>Kun je mij de Nederlandse uitleg mailen aub, ook ik wil je graag na doen in het maken, van 0v tot 20v of meer zelfs als dat kan 35/40v Mischien </p>
      <p>Sorry mijn email is. wannaduino@gmail.com</p>
      <p>Hi there, nice Instructable! I hope you can help me to reproduce it.</p><p>I just copied your code but I get an error in Processing: I get a message saying &quot;Null Pointer Exception&quot; and line 15 [&quot;PFont font= createFont(&quot;Lucida Console&quot;, 12, false);]. It's not clear if the rest of the code is OK or if it has stopped verifying in the first error.</p><p>Any idea how I can correct this? It's my first time using Processing (v3.0.1).</p><p>Tks.</p>
      <p>Hi Rbalani,</p><p>It could be the font that is missing. Try:</p><blockquote>PFont font= createFont(&quot;Arial&quot;, 12, false);</blockquote><p>Also, in Processing 3:</p><blockquote>frame.setResizable(true);</blockquote><p>should become:</p><blockquote>surface.setResizable(true);</blockquote><p>Good luck!</p>
      <p>still error sir, what can i do?</p>
      <p>Sorry, I hadn't tested it in P3. <br>Now I have, and I've just added and updated scopeP3.pde to the instructable. Please let me know if it still doesn't work.</p>
      <p>it's work, thank you very much. </p>
      <p>Is this low cost? How much would it take for me to make this?</p>
      <p>Hi, dependent where you buy your stuff it will cost about $5-10.</p>
      <p>Then is there any way I can make a lowcost oscillator that can display analog and digital signals?</p>
      <p>An oscillator generates a signal. With a scope you can make the signals visuable.For this project is not stand alone. You need a PC to make the scope signals visuable.</p><p>For the Arduino there are a lot of projects to make these, generators and scopes. For a generator example see &quot;https://www.instructables.com/id/Arduino-Waveform-Generator/&quot;.</p>
      <p>so does it mean this can display both analog and digital waves? sorry I'm new to arduino. As in very new. It just happened that I watched a youtube video &quot;Poor man's oscilloscope&quot;, and it said that it can only display rectangular waves.</p>
      <p>Hello Ebud, it simply plots the voltage measured at the probe. So digital signals would look like a rectangular wave (either ON or OFF - 1 or 0). Analog signals (like in the screenshot above) can be anything in between.</p>
      <p>Sorry, I cannot answer your question because I don't enough of arduino as scope. Till now I do experiments with the arduino in temp and humanidy messures. </p>
      Great Instructable! <br>It may be a good idea to add a 5.1V zener diode on the Arduino's inputs, or even an op-amp buffer, just in case ...
      <p>Thanks, tttapa!</p><p>Do you mean a zener between A1 and GND (parallel to the 1K resistor)? <br>I was thinking about that, but afraid it might affect the readout.<br>(but my knowledge on electronics is very limited...)</p>

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